Similar as in the section Piling Cylindrical Catalysts we want to add the user-defined objects created in the previous section as catalysts in the reactor.

1. Select Results-User as the project folder (File → Choose Project Folder → Select Project Folder) if it is not already done and open the Reactor.gdt file from the Results-User folder.
   
2. Select Model → GrainGeo from the menu bar.
   
3. Select Pile Grains from the drop-down menu in the GrainGeo module section and click Edit….
   
4. In the GrainGeo Pile Options dialog, change the Result File Name to Pile-Cylinder-4-holes.gdr.
5. In the Pile Options tab adjust the following settings:
   1. Check Pile in Current Domain and Keep Current Objects/Structure. In this way, the reactor is preserved and the objects will be piled inside the tube.
   2. Make sure, that Prohibit Object Overlap and Fill To Rim are selected at the bottom of this tab.
   3. As Random Seed choose 47.
      
6. In the Object Options tab, Remove the predefined objects and Add a Combined Object. Click Browse… to search for the file Cylinder-4-holes.gad.
   
7. Do not change anything in the Object Motion and Result Options tabs.
8. Click OK to close the GrainGeo Pile Options dialog and click Generate to start the piling process.
   

After the run is finished, the model of the bed reactor, packed with the cylinders with 4 holes, appears in the Visualization area. You can set the Structure Renderer (see Visualization Settings) from Smooth to Box to better observe the piled objects.